This study analyzes grammatical and structural characteristics of English NPs based on X`-scheme rather than phrase structure rules because the phrase structure rules have some problems in showing grammatical characteristics of English NPs when compared to X`-scheme that allows an intermediate projection in the phrase structure. Furthermore, by introducing X`-scheme, we could explain the differences of structural and lexical ambiguities from some English NPs, and say that when the auxiliary verb of subject-auxiliary inversion, and the wh-element in the interrogative sentence are moved to the initial position of sentence, they keep the ``structure preserving hypothesis.`` In addition, X``-scheme seems to be expected to help Korean students in class really understand English NPs better. (Youngnam Cyber University)